In optical transmitters, optical modulators are used to modulate optical carriers (light beams) with analog or digital signals for transmission through optical fibers. A typical wavelength division multiplexing-based optical transmitter uses several lasers each operating at a different wavelength to generate several different optical carriers. Each carrier passes through its own optical modulator where it is modulated with a signal to be transmitted. Then the modulated carriers are fed through an optical multiplexer into an optical fiber for transmission. As one of some attractive silicon-based optical modulator designs, a silicon MOS capacitor adjoins a silicon optical waveguide. A signal applied across the capacitor induces an accumulation of charge near the center of the capacitor. This accumulation of charge modifies the-refractive index of the optical waveguide as well as its propagation loss. Modifying the refractive index causes a phase shift in a beam of light propagating through the waveguide, thereby phase-modulating the light. When phase shift is utilized in optical waveguide components such as Mach-Zehnder interferometers (MZI), ring resonators, or Fabry-Perot (FP) resonators, the optical waveguide component transforms optical phase shift into optical power change to realize optical intensity modulation. When analog or constant optical power reduction is the purpose instead of coding an electrical signal into an optical signal, the optical modulator can be used as an optical attenuator.